"It was an initial incident involving at least two to three people. As Jesse has gone towards the car park at McDonald's he's been followed by two of the three people, we believe, and one of those two has assaulted Jesse."

He added: "It appears Jesse has been the victim of a serious assault and has suffered head injuries as a result."

Archer said he expected to have "reasonable footage" of the people available from CCTV cameras.

Ryder had been drinking with his Wellington team-mates in the bar, though it appears this was not a factor in the incident.

Archer said there were "at least 10 or more witnesses" and while the people involved had not been identified there were "positive lines of inquiry".

Ryder, a controversial figure whose career has been plagued by off-field incidents, is on an indefinite break from international cricket and has not played for New Zealand since February last year.

He has admitted in the past that alcohol has contributed to his off-field problems.

New Zealand Cricket Players' Association chief executive Heath Mills said today: "Jesse has been fighting some demons over the years and he has struggled with them. It will be an ongoing battle for Jesse and we need to do all we can to help him.

"He's got those demons so it shouldn't be a surprise if in the future if we have to deal with isolated incidents.

"What I will say - and it's been made very clear to us by the police today - is that Jesse was having a few drinks with his team-mates at the conclusion of their season. The actual assault was not an alcohol-fuelled incident."

New Zealand Cricket offered its support to the player.

"We are all shocked by what has occurred and extremely concerned for Jesse. New Zealand Cricket's thoughts are with him and his family," NZC chief executive David White said.

Former England captain Michael Vaughan posted: "Devastating news regarding Jesse Ryder... Just hope he can pull through... Thoughts are with him and his family..."

Ryder has played 18 Tests and 39 one-day internationals for the Black Caps, his last appearance an ODI against South Africa.

He played yesterday for the Wellington Firebirds in the major preliminary final against Canterbury Wizards at Hagley Oval and was due to fly out to India this week to compete for the Delhi Daredevils in the Indian Premier League.